Try to disconnect Sync and change the password of the Firefox Account to reset all data on the Sync server.

If you use Sync then best is to disconnect Sync temporarily during troubleshooting.

You can check for problems with the places.sqlite and favicons.sqlite files in the Firefox profile folder.

• use "Verify Integrity" button on the "Help -> Troubleshooting Information" (about:support) page

In case errors are reported with "Verify Integrity" close and restart Firefox and retry.

If "Verify Integrity" cannot repair places.sqlite, rename/remove all places.sqlite and favicons.sqlite files in the Firefox profile folder. Firefox will rebuild places.sqlite and restore the bookmarks from a recent JSON backup in the bookmarkbackups folder.

• keep a backup copy of places.sqlite in case a new places.sqlite database has to be created

See also:

• https://support.mozilla.org/en-US/kb/Bookmarks+not+saved#w_fix-the-bookmarks-file
• https://support.mozilla.org/en-US/kb/fix-bookmarks-and-history-will-not-be-functional

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Folder/Directory:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/Profiles

If you use Sync then best is to reconnect one device at the time and wait for the initial Sync to finish before connecting another device once you have fixed the bookmarks.

I developed my own solution for this issue: I turned off Sync on all devices. Couldn't figure out how to do that on my phone, so I simply uninstalled the app completely from that one. Then, I went in to the desktops and laptop, and deleted all bookmarks. After deleting all of the bookmarks, I restored my bookmarks from a time recently before I turned sync on. It was easy enough to identify an early enough backup, because the size of the file was *half* of all of the newer ones... After doing that, I turned sync back on, and hit the sync button. Then, I turned sync on for my other machines, one at a time, and they grabbed my latest bookmarks from the first machine, without doubles...After finishing those, I reinstalled the app on my phone, and that one did the same as the others. I did change the sync settings a bit- I removed sync for history, as there was a crazy amount of data there, and I didn't see the need to have that carry over from one device to the next.

...so far, so good...

Thanks

edited by a moderator to remove the line indents which mess up the formatting in this software and make it harder to read without horizontal scrolling

I've had a similar issue in the past. But this was actually being caused by the fact that I had a tool installed in an alternative browser, to help me sync my bookmarks across different browsers (the work computer was locked down and firefox wasn't allowed). got rid of this and sync worked fine.

No other sync software installed. It was just an odd issue that appeared as soon as I decided to sync FF across all of my devices.

Firefox for Android or Firefox for iOS is typically the cause of duplicated bookmarks on laptop / desktop installations.

No IOS here. As mentioned above, I developed my own solution, which is working fine currently. If the doubled bookmarks return, I will post here, but for now, it's been solved in the following way:

I turned off Sync on all devices. Couldn't figure out how to do that on my phone, so I simply uninstalled the app completely from that one.  Then, I went in to the desktops and laptop, and deleted all bookmarks.

After deleting all of the bookmarks, I restored my bookmarks from a time recently before I turned sync on. It was easy enough to identify an early enough backup, because the size of the file was *half* of all of the newer ones... After doing that, I turned sync back on, and hit the sync button. Then, I turned sync on for my other machines, one at a time, and they grabbed my latest bookmarks from the first machine, without doubles...After finishing those, I reinstalled the app on my phone, and that one did the same as the others.